How To Troubleshoot MacOS No-access
The Basics of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address like 230.130.190.43 or an IPv6 address like 2000:ce67:feea:3584:eaf5:c9dd:fe05:72c3. You can verify this information by visiting https://test-ipv6.com/. However, attempting to convey these addresses to individuals who are not technologically inclined, or even referencing MAC addresses like 9e:ee:89:7f:08:61, can lead to errors and complications. Furthermore, these addresses do not provide historical data, particularly from past issues.
Navigating the World Wide Web
In order to access a web page such as https://jacobs-fisher.org, your computer initially contacts a DNS server to convert the host portion (jacobs-fisher) combined with the Top Level Domain (org) of the URL to an IP address like 182.240.13.35. Furthermore, your computer and browser transmit their type with each web request, for instance: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
Understanding the Significance of Default Gateways
The default gateway, typically obtained through DHCP, is an automatically configured address such as 192.0.0.45 (although they typically end in .1 or .254 based on the scope size). This is the location where your computer directs all of its traffic to be routed. For information on troubleshooting IPv6 connectivity, we offer an in-depth guide on how-to-fix-ipv6-connectivity/ or you can verify on Mac or Linux by using the command:
IPv4 Routes and the Host IPv4 Route Table (inc. VPN)
netstat -rn -f inet | egrep -i "default|0/1|128.0/1"
0/1 172.18.12.193 UGScg utun3 default 192.0.0.45 UGScg en0 128.0/1 172.18.12.193 UGSc utun3
Note: We are not just looking for the default but also for any VPN that overrides the public v4 address space.
IPv6 Routes and the Host IPv6 Route Table (inc. VPN)
netstat -rn -f inet6 | egrep -i "default|2000::/3"
If you have IPv6 active the above should return at least one route (as per below) via a known interface such as “en0 " on a Mac.
default fe80:789:c5c8:c65:8229%en0 UGcg en0 default fe80::%utun0 UGcIg utun0 default fe80::%utun1 UGcIg utun1 default fe80::%utun2 UGcIg utun2 2000::/3 utun3 USc utun3
Note: We are not just looking for the default but also for any VPN that overrides the public v6 address space.
Debugging DHCP for both IPv4 and IPv6
To get a look at the low level DHCP configuration (Mac/Linux):
ipconfig getpacket en0
...
domain_name_server (ip_mult): {233.119.222.157, 89.131.51.203}
end (none):
...
So, in the above we are not getting IPv6 DNS servers from the DHCPv4 reply but…
ipconfig getv6packet en0
DHCPv6 REPLY (7) Transaction ID 0x80940b Length 76
Options[4] = {
CLIENTID (1) Length 14: DUID LLT HW 1 Time 668691856 Addr 9e:ee:89:7f:08:61
DNS_SERVERS (23) Length 32: 2606:4700:4700::1111, 2001:4860:4860::8844
DOMAIN_LIST (24) Length 0: Invalid
SERVERID (2) Length 10: DUID LL HW 1 Addr 74:46:69:f6:9e:be
}
Resolving Issues with Wired and Wireless Connections
When it comes to sending data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Actions for Apple macOS / OSX Troubleshooting
Regardless of whether you are running OSX/macOS version 10.15.9, 11.2.7, or 12.1.5, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams that are adopting remote work and Work From Anywhere (WFA).
Useful In-Built Scripts
One valuable tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can also generate specific logs for troubleshooting purposes. Another comprehensive tool is the sysdiagnose tool, which can generate a wide range of logs, although many of them are only relevant to wireless at a specific point in time, similar to wdutil.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose and it will display a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. However, be aware of the file sizes, which are approximately 300MB.
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